KR20110116019A - Battery electrolyte solutions containing aromatic phosphorus compounds - Google Patents

Abstract

The battery electrolyte of the present invention contains 0.01 to 80% by weight of aromatic phosphorus compounds. The aromatic phosphorus compounds provide increased thermal stability to the electrolyte, helping to reduce thermal decomposition, thermal runaway reactions, and the likelihood of combustion. Such aromatic phosphorus compounds have little negative effect on the electrical properties of the cell and in some cases actually improve the cell performance.

Description

Battery electrolyte containing an aromatic phosphorus compound {BATTERY ELECTROLYTE SOLUTIONS CONTAINING AROMATIC PHOSPHORUS COMPOUNDS}

The present invention claims priority to US Provisional Application No. 61 / 140,579, filed December 23, 2008.

The present invention relates to a non-aqueous electrolyte containing an aromatic phosphorus additive.

Lithium batteries are widely used as primary and secondary batteries for vehicles and many types of electronic equipment. Such cells tend to have high energy and power densities and are therefore preferred for many applications. The electrolyte in a lithium battery is of non-aqueous type as needed. Such non-aqueous electrolytes are generally high dielectric content solutions of lithium salts in organic solvents or mixtures of organic solvents. Various linear and cyclic carbonates are commonly used, but certain esters, alkyl ethers, nitriles, sulfones, sulfolanes, sultones, and siloxanes can also act as solvents. In many cases, the solvent may contain two or more of these materials. Polymer gel electrolytes are also known.

Such electrolytes are sensitive to high temperatures because they contain high concentrations of organic materials. The electrolyte may decompose, be involved in exothermic runaway reactions, or even burn if exposed to the wrong conditions. Lithium batteries are known to ignite due to overcharge, overdischarge, short circuit conditions and mechanical or thermal misuse. In addition to combustion, other problems can occur, for example, significant losses in battery life. Therefore, additives have been incorporated into the electrolyte of the lithium battery to help stabilize the electrolyte.

Many phosphorus compounds have been proposed as flame retardants or "thermal runaway inhibitors" for battery electrolytes. The compounds include various phosphine oxides (O: PR ₃ ), phosphinite (P (OR) R ₂ ), phosphonite (P (OR ₂ ) R), phosphite (P (OR) ₃ ), phosphi Nate (O: P (OR) R ₂ ), phosphonate (O: P (OR) ₂ R), phosphate (O: P (OR) ₃ ) and phosphazene (-N = PR _2- ) _n compounds Include.

The phosphorus compound was not completely satisfactory. Some of these must be added in very excess in order to be effective. Other compounds react with other additives in non-aqueous solvents, lithium salts or electrolytes, or with anode or cathode materials. Another compound negatively affects cell performance. It is desirable to provide additives for non-aqueous cell electrolytes that provide good stability at an appropriate level, do not negatively interact with other components or anodes or cathodes in the electrolyte, and have little or no negative impact on cell performance. something to do.

In one embodiment, the invention is a battery electrolyte comprising at least one lithium salt and a non-aqueous solvent, wherein the lithium salt is soluble, and 0.01-80% by weight of the battery electrolyte is at least one aromatic of formula (I) Phosphorus compound is:

[Formula I]

Where

A ¹ is a radical containing one or more aromatic rings,

Each R is, independently, an alkylene divalent radical which may contain 1 to 3 carbon atoms and is directly bonded to the carbon atom of the aromatic ring of the A ¹ group,

R ¹ is each independently hydrogen, halogen, OH, a hydrocarbyl group having 12 or less carbon atoms, or an alkoxyl group having 12 or less carbon atoms, or a ring structure in which two R ¹ groups attached to the same phosphorus atom together contain a phosphorus atom Form the

x is an integer of 2 or more.

The invention also relates to a battery comprising an anode, a cathode, a separator disposed between the anode and the cathode, and a non-aqueous battery electrolyte in contact with the anode and the cathode, wherein the battery electrolyte comprises at least one lithium salt, A non-aqueous solvent in which the lithium salt is dissolved, wherein about 0.01 to 80% by weight of the battery electrolyte is at least one aromatic phosphorus compound of formula (I).

Aromatic phosphorus compounds as described herein provide excellent thermal stabilization for the cell electrolyte. The battery electrolyte tends to be resistant to thermal decomposition, is less involved in thermal runaway reactions, and is resistant to combustion. Surprisingly, the aromatic phosphorus compounds sometimes substantially increase cell capacity utilization, discharge rate performance and / or cycle stability of the cell.

In certain preferred embodiments, the battery electrolyte further comprises (a) at least one phosphorus-sulfur compound as described below, (b) at least one carbonate compound containing at least one aliphatic carbon-carbon double bond, (c) one Or a sultone compound, or (d) a mixture of any two or more of the foregoing compounds. Batteries containing such a preferred electrolyte solution tend to have particularly excellent cycle stability, and in this case, the thermal stability of the electrolyte solution tends to be maintained very well even after repeated cycles.

1 is a graph of 4C discharge curves of two cells and three comparative cells according to the present invention.
2 is a graph of 4C discharge curves of three cells and three comparative cells according to the present invention.
3 is a graph of 4C discharge curves of two cells and two comparative cells according to the present invention.
4 is a graph of 4C discharge curves of three cells and one comparison battery according to the present invention.

The R ¹ groups in formula (I) may each independently be different, preferably an alkoxyl group having 8 or less carbon atoms, more preferably 4 or less carbon atoms, even more preferably 1 to 3 carbon atoms. Alkoxyl R ¹ groups may be linear or branched and may contain substituents such as halogen (especially fluorine, chlorine or bromine) or alkoxyl. Two alkoxyl R ¹ groups attached to a phosphorus atom may together form a ring structure comprising a phosphorus atom. Such ring structures can be represented by the following formula (II):

≪ RTI ID = 0.0 &

Where

R ² is an alkylene divalent radical which may be substituted with an ether linking group, a halogen or an alkoxyl group.

Particularly preferred R ¹ groups in formula (I) are methoxyl, ethoxyl, isopropoxyl and n-propoxyl.

The R groups in formula (I) are each preferably methylene (-CH _2- ), ethylene (-CH ₂ -CH _2- ) or isopropylene (-CH ₂ -CH (CH ₃ )-), with methylene being most preferred. . Each R group in formula (I) is bonded directly to the carbon atom of the aromatic ring of said A ¹ radical.

The A ¹ radical of formula (I) contains one or more aromatic rings. It may contain two or more aromatic rings. When multiple aromatic rings are present, these rings are linked as fused ring structures (e.g., naphthalene), covalently linked (e.g., biphenyl compounds), or linked via one or more aliphatic or alicyclic groups, or hetero Atom-containing groups (eg, ether, ester, amino, amido, carbonate, or —SO ₂ — linking groups).

The aromatic ring contained in the A ¹ radical may include a substituent in addition to the group —RP (O) — (R ¹ ) ₂ , and may include any linking group for another ring. Examples of such substituents are halogen, hydroxyl, straight or branched chain alkyl (preferably containing up to 4 carbon atoms), alkoxyl (preferably containing up to 4 carbon atoms), or straight or branched chain alkenyl (Preferably containing up to 4 carbon atoms).

Preferred aromatic phosphorus compounds have the structure of formula III:

[Formula III]

Where

R ³ are each independently, hydrogen, hydroxyl, halogen, C _{1 -3} alkyl, alkoxyl having 1-3 carbon atoms, or C _{2 -3} alkylene,

R, R ¹ and x are as defined in formula (I) above.

R ³ is most preferably hydrogen or a C _{1 -3} alkyl.

The value of x is preferably 2 to 4, more preferably 2 or 3.

Among useful classes of aromatic phosphonate compounds are compounds of formula IV or V

[Formula IV]

[Formula V]

In each case, R ⁴ is each independently alkyl having 1 to 8 carbon atoms, preferably 1 to 4 carbon atoms, more preferably 1 to 3 carbon atoms, and R ³ is as defined in Chemical Formula III. .

Preferably, in formula IV and V R ⁴ are each independently a methyl, ethyl, or isopropyl, R ³ are each preferably a hydrogen or a C _{1 -3} alkyl. The phosphonate groups in formula (IV) may be in the 1,2,3-, 1,2,4- or 1,3,5-position of the benzene ring when one of them is taken in position 1. The phosphonate groups in formula (V) may be in the ortho, meta or para position relative to each other in the benzene ring.

Particular aromatic phosphorus compounds useful in the present invention include structures of the following formulas VI-XI.

[Formula VI]

[Formula VII]

(VIII)

(IX)

[Formula X]

(XI)

Particular preference is given to aromatic phosphorus compounds of the above formulas VI and X.

Mixtures of two or more of these aromatic phosphorus compounds may be used. Of particular interest are mixtures of from 10 to 95% by weight of an aromatic phosphorus compound of formula III, wherein the x value is at least 3, preferably 3 or 4, and from 5 to 90% by weight of second aromatic phosphorus of formula III Is a mixture of compounds, wherein the value of x is 2. The weight ratio of these two aromatic phosphorus compounds is preferably 30:70 to 70:30, or 40:60 to 60:40 (weight ratio). The presence of such a mixture has been found to make the battery electrolyte more storage stable compared to the case where all of the compounds of formula III have x equal to or greater than 3.

The aromatic phosphorus compound may account for about 0.01 to 80% of the total weight of the battery electrolyte. However, an advantage of the present invention is that it is generally effective even when the aromatic phosphorus compound is added at a low level. Therefore, the aromatic phosphorus compound preferably accounts for 15% or less, more preferably 10% or less of the total weight of the battery electrolyte. Particularly preferred amounts are up to 5% of the total weight of the battery electrolyte. The lower limit is preferably at least 0.1% of the total weight of the electrolyte.

Other major components of the battery electrolyte are lithium salts and non-aqueous solvents for the lithium salts.

The lithium salt may be any suitable for use in a battery, for example inorganic lithium salts such as LiAsF ₆ , LiPF ₆ , LiB (C ₂ O ₄ ) ₂ , LiBF ₄ , LiBF ₂ C ₂ O ₄ , LiClO ₄ , LiBrO ₄ and LiIO ₄ ; And organic lithium salts such as LiB (C ₆ H ₅ ) ₄ , LiCH ₃ SO ₃ , LiN (SO ₂ C ₂ F ₅ ) ₂ and LiCF ₃ SO ₃ . LiPF ₆ , LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ and LiN (SO ₂ CF ₃ ) ₂ are the preferred types, and LiPF ₆ is a particularly preferred lithium salt.

The lithium salt is suitably present at a concentration of at least 0.5 mol / L, preferably at least 0.75 mol / L, at most 3 mol / L, more preferably at most 1.5 mol / L of the electrolyte.

The non-aqueous solvent may include, for example, one or more linear alkyl carbonates, cyclic carbonates, cyclic esters, linear esters, cyclic ethers, alkyl ethers, nitriles, sulfones, sulfolanes, siloxanes and sultones. Mixtures of any two or more of the aforementioned types can be used. Cyclic esters, linear alkyl carbonates and cyclic carbonates are the preferred types of non-aqueous solvents.

Suitable linear alkyl carbonates include dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate and the like. Suitable cyclic carbonates include ethylene carbonate, propylene carbonate, butylene carbonate and the like. Suitable cyclic esters include, for example, γ-butyrolactone and γ-valerolactone. Cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran and the like. Alkyl ethers include dimethoxyethane, diethoxyethane and the like. Nitriles include mononitriles such as acetonitrile and propionitrile; Dynitrile such as glutaronitrile; And derivatives thereof. Sulfones are symmetrical sulfones such as dimethyl sulfone, diethyl sulfone and the like; Asymmetric sulfones such as ethyl methyl sulfone, propyl methyl sulfone and the like; And derivatives thereof. Sulfonanes include tetramethylene sulfolane and the like.

Some preferred solvent mixtures include mixtures of cyclic carbonate / linear alkyl carbonates in a weight ratio of 15:85 to 40:60; Mixture of cyclic carbonate / cyclic ester in a weight ratio of 20:80 to 60:40: a mixture of cyclic carbonate / cyclic ester / linear alkyl carbonate in a weight ratio of (20 to 48) :( 50 to 78) :( 2 to 20); Mixtures of cyclic ester / linear alkyl carbonates in a weight ratio of 70:30 to 98: 2.

Particularly interesting solvent mixtures include mixtures of ethylene carbonate / propylene carbonate in a weight ratio of 15:85 to 40:60; Mixtures of ethylene carbonate / dimethyl carbonate in a weight ratio of 15:85 to 40:60; A mixture of ethylene carbonate / propylene carbonate / dimethyl carbonate in a weight ratio of (20 to 48) :( 50 to 78) :( 2 to 20); Propylene carbonate / dimethyl carbonate in a weight ratio of 15:85 to 40:60.

In addition to the components mentioned above, various other additives may be present in the battery electrolyte. Such additives include, for example, additives which promote the formation of a solid electrolyte interface at the surface of the graphite electrode; Various cathode protectants; Lithium salt stabilizers; Lithium deposition improvers; Ionic solvation improvers; Corrosion inhibitors; Wetting agents; Flame retardant; And viscosity reducing agents. Many additives of this type are described in Zhang in "A review on electrolyte additives for lithium-ion batteries," J. Power. Sources 162 (2006) 1379-1394.

Agents that promote the formation of a solid electrolyte interface (SEI) include various polymerizable ethylenically unsaturated compounds, various sulfur compounds, and other materials. Suitable cathode protectants include materials such as N, N-diethylaminotrimethylsilane and LiB (C ₂ O ₄ ) ₂ . Lithium salt stabilizers include LiF, tris (2,2,2-trifluoroethyl) phosphite, 1-methyl-2-pyrrolidone, fluorinated carbamate and hexamethylphosphoamide. Examples of lithium deposition improvers include sulfur dioxide, polysulfide, carbon dioxide; Surfactants such as tetraalkylammonium chloride; Lithium and tetraethylammonium salts of perfluorooctanesulfonate; Various perfluoropolyethers and the like. Crown ethers may be suitable ionic solvation improvers, and various borate, boron and borol compounds are also suitable. LiB (C ₂ O ₄ ) ₂ and LiF ₂ C ₂ O ₄ are examples of aluminum corrosion inhibitors. Cyclohexane, trialkyl phosphates and certain carboxylic acid esters are useful as wetting agents and viscosity reducing agents. Some materials, such as LiB (C ₂ O ₄ ) ₂ , can perform multiple functions in the electrolyte.

Various other additives may together comprise up to 20%, preferably up to 10%, of the total weight of the battery electrolyte.

The electrolyte solution containing the compound of formula III may contain an aromatic monophosphate compound corresponding to formula XII:

(XII)

Wherein R ³ , R and R ¹ are as defined in Formulas I and III, respectively.

When x is 3 or more in the compound of formula III, it is preferred that a compound of formula XII is present. The weight ratio of the compound of formula III to the compound of formula XII may be 10:90 to 95: 5, preferably 30:70 to 70:30, or 40:60 to 60:40. When the compound of formula XII is present together with the compound of formula III (where x is 3 or more), the battery electrolyte is more storage stable than when only the compound of formula III (where x is 3 or more) is present. Turned out. Examples of suitable compounds of formula XII are compounds of formulas XIII to XVIII.

(XIII)

(XIV)

(XV)

(XVI)

Formula XVII]

[Formula XVIII]

Preferred battery electrolytes include (a) one or more phosphorus-sulfur compounds, (b) one or more carbonates containing aliphatic carbon-carbon unsaturated groups, (c) one or more sultone compounds, or (d) any two of the aforementioned components It contains the above mixture. When one or more such compounds are present, it has been found that the cycle stability of the cells containing such electrolytes and the thermal stability of the electrolytes after cycles are significantly improved. These compounds, individually or in total, may account for 0.001 to 20% of the total weight of the battery electrolyte. Based on the total weight of the battery electrolyte, the lower limit is preferably 0.01% by weight or more, and the upper limit is preferably 10% by weight.

Suitable phosphorus-sulfur compounds are described in WO 08/88487, the disclosure of which is incorporated herein by reference. Such phosphorus-sulfur compounds are represented by the formula: XIX:

[Formula XIX]

Where

X is oxygen or sulfur,

T is a covalent bond, oxygen or sulfur, provided that at least one of X and T is sulfur,

Each X 'is independently oxygen or sulfur,

each m is independently 0 or 1 when X 'is oxygen, 0, 1 or 2 when X' is sulfur,

n is 1 or more, preferably 2 or more,

Each R ⁵ is, independently, an unsubstituted or inactively substituted hydrocarbyl group, or the R ⁵ groups together form an unsubstituted or inactively substituted divalent organic group,

A is an organic linking group.

Certain useful types of suitable phosphorus-sulfur additives can be represented by the following structural formulas XX, XXI and XXII:

[Formula XX]

[Formula XXI]

[Formula XXII]

Wherein R, X, T, A and n are as described above in formula XIX, and at least one of X and T is sulfur.

T in the formulas XIX, XX, XXI and XXII is preferably oxygen or sulfur, most preferably sulfur. X is preferably sulfur and n is preferably 2 or more. The R ⁵ group in formula XIX, XX, XXI or XXII can be, for example, an unsubstituted or inertly substituted aliphatic, alicyclic or aromatic group. A "inactive" substituent is a substituent that does not interfere much with the SEI-forming properties of the additive. Such inert substituents can be, for example, oxygen-containing groups such as ether, ester, carbonyl or oxirane groups and the like. Inert substituents may be nitrogen-containing groups such as primary, secondary or tertiary amine groups, imine groups, amide groups or nitro groups. The inert substituents may contain other hetero atoms such as sulfur, phosphorus and the like.

For the purposes of the present invention, hydrocarbyl groups are groups containing only hydrogen and carbon atoms. Hydrocarbyl groups may be aliphatic, cycloaliphatic, aromatic, or some combination of two or more of these types.

The R ⁵ group in formula XIX, XX, XXI, or XXII is preferably an unsubstituted or inertly substituted lower alkyl such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, secondary- Butyl, tert-butyl and the like. In another preferred embodiment, such as illustrated by the general formula XXIII for example, two R ⁵ groups together, and each _{- (X ') m -P- (} X') m -, -OPO-, -SPO- or To form a divalent organic radical which completes the -SPS- linking group.

Particularly preferred phosphorus-sulfur additives are the compounds represented by the formula (XXIII):

[Formula XXIII]

Where

X, n and A are as described for Formula XIX (X is preferably sulfur),

Each R ⁶ is independently hydrogen, alkyl or inactively substituted alkyl,

R ⁷ is a covalent bond or a divalent linking group.

In formula (XXIII), the R ⁶ group is preferably hydrogen or lower alkyl, more preferably hydrogen. The R ⁷ group is preferably a straight or branched chain hydrocarbyl group, —O— or a covalent bond. More preferred R ⁷ groups are hydrocarbyl groups disubstituted on the same carbon on carbon atoms or carbon atoms directly bonded to the R ⁶ ₂ C group. The R ⁷ group is most preferably dialkyl-substituted methylene, even most preferred when the R ⁷ group is (dimethyl) methylene.

Particularly preferred types of phosphorus-sulfur additives are represented by the formula XXIV:

Formula XXIV

Wherein X, n and A are as described above in formula (XIX).

X is preferably sulfur.

In the formulas XIX to XXIV, the A group is an organic linking group. Such organic linking groups may have a variety of possible structures. The organic linking group is covalently bonded to a -T- linking group (in formulas XIX to XXII) or an -S- atom (in formulas XXIII and XXIV). The -T- or -S- linking group may be bonded to a carbon atom or heteroatom on the organic linking group A, but is preferably bonded to a carbon atom. The carbon atom is preferably a primary or secondary carbon atom (ie bonded to one or two other carbon atoms), but less preferably a tertiary carbon atom (ie bonded to three other carbon atoms) )to be.

One type of such organic linking group A is an unsubstituted or inertly substituted hydrocarbyl group. The organic linking group A may contain any number of carbon atoms, but preferably a molecular weight per phosphorus atom does not exceed about 1000 Da, more preferably does not exceed about 750 Da, in particular less than 500 Da to be. The phosphorus-sulfur additive may contain 5 to 50 wt.% Sulfur. The organic linking group A may be aliphatic (linear or branched), alicyclic, aromatic, or some combination thereof. The valence of A in the organic connection is equal to n.

One preferred type of the linking group A in the formulas XIX to XXIV is bonded to a -T- or -S- linking group (optionally) via a benzyl carbon atom. Particular examples of phosphorus-sulfur additives containing this type of A group are compounds of the formulas XXV to XXXIV.

[Formula XXV]

Formula XXVI

Formula XXVII

Formula XXVIII

[XXIX]

[Formula XXX]

[Formula XXXI]

[Formula XXXII]

[Formula XXXIII]

[Formula XXXIV]

In the case of the phosphorus-sulfur group, it is also possible to directly bond to the aromatic ring of the A group.

Suitable carbonate compounds having aliphatic carbon-carbon unsaturated groups include vinylidine carbonate, vinyl ethyl carbonate, allyl ethyl carbonate, and the like.

The sultone compound is a cyclic sulfonate ester of hydroxyl sulfonic acid. This can be represented by the following formula XXXV:

[Formula XXXV]

Wherein R ⁸ is an alkylene group such that the ring structure contains 5 to 7 atoms.

R ⁸ groups may be substituted with alkyl groups. Examples of suitable sultone compounds are 1,3-propane sultone.

The battery electrolyte is conveniently prepared by dissolving or dispersing the lithium salt, the aromatic phosphorus compound, and any other additives that may be used in the non-aqueous solvent. In general, the mixing order is not important. The water content of the resulting cell electrolyte should be as low as possible. A water content of 50 ppm or less is preferable, and a water content of 30 ppm or less is more preferable. In order to remove the residual amount of water, these various components may be individually dried and / or the combined electrolyte may be dried before the electrolyte is formed. The drying method chosen should not degrade or decompose the various components of the electrolyte and should not promote undesirable reactions between these components. Thermal methods can be used, and drying agents (eg molecular sieves) can also be used.

The battery containing the electrolyte solution of the present invention may be of any useful structure. Typical cell structures include an anode, a cathode, and a separator and electrolyte disposed between the anode and the cathode, through which ions can migrate through the electrolyte between the anode and the cathode. Such assemblies are generally packaged in a case. The form of the battery is not limited. The battery may be cylindrical having a spirally wound sheet electrode and a separator. The battery may be cylindrical having an inside-out structure including a combination of a pellet electrode and a separator. The battery may be a plate-type containing an overlapping electrode and a separator.

Suitable anode materials include, for example, carbonaceous materials such as natural or artificial graphite, carbonized pitch, carbon fibers, graphitized mesophase microspheres, furnace black, acetylene black and various other graphitized materials. The carbonaceous material may be a binder (eg poly (vinylidene fluoride), polytetrafluoroethylene, styrene-butadiene copolymer, isoprene rubber, poly (vinyl acetate), poly (ethyl methacrylate) ), Polyethylene or nitrocellulose). Suitable carbonaceous anodes and methods for their preparation are described, for example, in US Pat. No. 7,169,511.

Other suitable anode materials include lithium metals, lithium alloys and other lithium compounds such as lithium titanate anodes.

Suitable cathode materials include inorganic compounds such as transition metal oxides, transition metal / lithium composite oxides, lithium / transition metal composite phosphates, transition metal sulfides, metal oxides, and transition metal silicates. Examples of transition metal oxides include MnO, V ₂ O ₅ , V ₆ O ₁₃ and TiO ₂ . Transition metal / lithium composite oxides include lithium / cobalt composite oxides having a base composition of approximately LiCoO ₂ ; Lithium / nickel composite oxide having a basic composition of approximately LiNiO ₂ ; And lithium / manganese composite oxide having a base composition of approximately LiMn ₂ O ₄ or LiMnO ₂ . In this case, a part of the cobalt, nickel or manganese may be replaced by one or two kinds of metals (for example, Al, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Mg, Ga or Zr). Can be replaced. Lithium / transition metal composite phosphates include lithium iron phosphate, lithium manganese phosphate, lithium cobalt phosphate, lithium iron manganese phosphate, and the like. Examples of useful metal oxides include SnO ₂ and SiO ₂ . Examples of useful metal silicates include lithium iron orthosilicates.

In general, the electrodes are each in electrical contact with or are formed on the current collector. Suitable current collectors for the anode are made of metal or metal alloys such as copper, copper alloys, nickel, nickel alloys, stainless steel and the like. Current collectors suitable for the cathode include those made of aluminum, titanium, tantalum, two or more alloys thereof, and the like.

 The separator is interposed between the anode and the cathode to prevent the anode and the cathode from contacting each other and causing a short circuit. The separator is conveniently manufactured from a nonconductive material. It must not be reactive with, or be soluble in, the electrolyte solution or any components of the electrolyte solution under operating conditions. Polymeric separators are generally suitable. Examples of suitable polymers for forming the separator include polyethylene, polypropylene, polybutene-1, poly-3-methylpentene, ethylene-propylene copolymers, polytetrafluoroethylene, polystyrene, polymethylmethacrylate, poly Dimethylsiloxane, polyethersulfone and the like.

The electrolyte solution should be able to pass through the separator. For this reason, the separator is generally porous, in the form of a porous sheet, nonwoven or woven fabric. The porosity of the separator is generally about 20% or more and about 90% or less. Preferred porosity is 30 to 75%. The pores generally have a largest dimension of 0.5 μm or less, preferably 0.05 μm or less. The separator is typically 1 μm or more in thickness, and may be 50 μm or less in thickness. Preferred thickness is between 5 and 30 μm.

The battery is preferably a secondary (rechargeable) lithium battery. In such cells, the discharge reaction involves dissolution or delithiation of lithium ions from the anode, and simultaneous incorporation of lithium ions into the cathode. In contrast, the charging reaction includes mixing lithium ions from the electrolyte solution to the anode. Upon charging, lithium ions are reduced on the anode side, while lithium ions in the cathode material dissolve in the electrolyte.

The presence of the aromatic phosphorus compounds described in the present invention improves cell stability and battery life by stabilizing the electrolyte against thermal decomposition and runaway reactions and / or by reducing the fire ability of the electrolyte. Thermal decomposition and runaway reactions can result from (1) physical damage to the cell (which can cause short circuits within the cell structure), (2) thermal misuse of the cell (this is mainly due to storage and / or manipulation of the cell under high temperature conditions). And (3) some circumstances, including electrical conditions such as overcharging or the generation of electrical shorts.

An overcharged environment can cause lithium to form a dendrite structure. The dendrite structure may extend through the electrolyte and through the separator between the cathode and the anode to cause a short circuit. Such a short circuit can cause a very large current to flow through the electrolyte over a very short time, releasing heat that can cause decomposition or even runaway reaction of the electrolyte. This runaway reaction may even cause ignition of the electrolyte in the absence of a flame retardant or thermal runaway inhibitor. Even if the electrolyte is not ignited, the heat released due to this runaway reaction can severely shorten the battery life.

Very surprisingly, it has been found that the presence of such aromatic phosphorus compounds can improve the capacity utilization efficiency, discharge rate performance and / or cycle stability, rather than negative effects.

Cycle stability can be assessed by operating the cell at a given charge / discharge rate for a fixed number of charge / discharge cycles and measuring the capacity of the cell at the start and end of the evaluation. If the battery continues to be charged and discharged, the capacity tends to drop. For example, after 100 1C charge / discharge cycles, the capacity of the cell often drops to 60-70% of the starting capacity. However, in addition to the aromatic phosphorus compound, the battery electrolyte may include at least one phosphorus-sulfur compound described above; Carbonates containing carbon-carbon unsaturated groups; And / or when containing sultone compounds, the cycle stability becomes quite good and often tends to preserve 80% or more capacity after 100 1C charge / discharge cycles.

The battery of the present invention can be used in industrial applications, for example electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, aerospace, e-bikes and the like. The batteries of the present invention also provide a number of electrical and electronic devices, such as computers, cameras, video cameras, mobile phones, PDAs, MP3 and other music players, televisions, dolls, video game players, home appliances, power tools, medical devices. For example, especially for manipulating cardiac pacemakers and defibrillators.

The following examples are provided to illustrate the invention but are not intended to limit the scope of the invention. Unless otherwise stated, all parts and percentages are by weight.

[Example]

In the following examples, the following aromatic phosphorus compounds are evaluated as additives.

Example  1 to 5 and Comparative Batteries A to F

A control cell electrolyte consisting of a 1.0 M solution of LiPF _{6 in} a 50/50 (volume ratio) mixture of ethylene carbonate / diethyl carbonate was prepared using LiCoO ₂ cathode, Mesocarbon Microbead (MCMB) graphite anode and polyolefin separator. Introduced in 2025 button cells. The button cell was designated as Comparative Battery A. Five 4C cycle curves were generated for Comparative Cell A using a Maccor 4000 cell tester and using two C / 10 cycles followed by five 4C cycles at ambient temperature. Representative discharge curves from this test were designated as curves “A” in FIGS. 1 to 4, respectively.

Battery Sample 1 was prepared in the same manner as above except that the electrolyte solution contained 5% by weight of APC1. The battery sample 1 was tested in the same manner as the comparative battery A. Representative discharge curves from these tests are shown as curves "1" in FIGS.

Battery Sample 2 was prepared in the same manner as Battery Sample 1, except that the electrolyte contained 5 wt% APC2 instead of APC1. Representative discharge curves are shown as curves "2" in FIGS.

Battery Sample 3 was prepared in the same manner as Battery Sample 1, except that the electrolyte contained 5 wt% APC3 instead of APC1. Representative discharge curves are shown as curve “3” in FIG. 2.

Comparative Cells B to F were prepared and tested in the same manner as in Battery Example 1, except that the electrolyte contained 5% by weight of APC4, APC5, APC6, APC7 and APC8 instead of APC1, respectively. Their representative discharge curves are presented as curves B and C in FIG. 1, curves D and E in FIG. 2, and curve F in FIG. 3, respectively.

The discharge curves in FIGS. 1 to 4 are normalized to the calculated charge capacity (the total amount of electrode material (in this case LiCoO ₂ cathode); The so-called "specific capacity"] illustrates the change in voltage produced by a cell when the cell is drained. The desired performance is for the battery to yield as much specific capacity as possible while the cell is drained within a specific voltage window (2.5 to 4.2 V in this case). In Figures 1-3, curve A drops to 2.5 V after the voltage produced by comparative cell A (which contains a control electrolyte without APC additive) is calculated for a specific capacity of about 75 to 80 mAh / g. Shows.

Battery Example 1 shows better performance in this discharge test despite the presence of 5% by weight of APC1. At 4C discharge rate, a specific capacity of more than 100 mAh / g was calculated by the battery within the voltage window.

In addition, Battery Example 2 also exhibited better performance than that of the control in this discharge test, although not as much as Battery Example 1. 1 to 3, curve 2 shows that cell sample 2 yields a specific capacity of 85 to 90 mAh / g within the specified voltage window. Together with the battery example 1, the presence of the aromatic phosphorus compound improves battery performance in comparison with the control (comparative battery A) in this discharge test.

Battery Example 3 showed only slightly poor performance in comparison with Comparative Sample A in this discharge test. Battery Example 3 calculated a specific capacity of 72 to 75 mAh / g within the voltage window.

Battery Example 3 showed better performance than each of Comparative Cells B through F in this test. For Comparative Cells B, C and E, the performance in the discharge test was worse than that of Battery Example 3, and for Comparative Battery F this performance was close to Battery Example 3 but still inferior.

Various examples and comparative samples show how the presence of phosphorus-based additives in the cell electrolyte can affect the electrical properties of the cell in an unexpected manner. In general, the addition of phosphorus-containing compounds has some negative effects, but the magnitude of these effects can vary considerably (eg, comparing the performance of Comparative Cells B, C, and D to Comparative Cells D and F and Cell Implementations). Compared to the performance of Example 1). However, the presence of the aromatic phosphorus compounds according to the invention can have a beneficial effect as in cell examples 1 and 2 or in most cases only a slight negative effect on specific capacity (as in cell example 3 and together). In addition, slight structural differences between the various phosphorus-containing compounds often have a very significant effect on the discharge curve (compare the results of Battery Example 2 with those of Battery Example 3, and compare the results of Comparative Cell E with Comparative Cell F By comparison with the results of).

Battery Example 1 was prepared again. For Cell Sample 1, which was prepared again, the 4C discharge curve was determined as above except this time using two C / 10 cycles followed by five cycles of C / 2, 1C, 2C and 4C, respectively. Representative discharge curves from this test are presented as curve “1” in FIG. 4.

Battery Example 4 was identical to Battery Example 1 except that only 1% by weight of APC1 was present. Battery Example 4 was tested in the same manner as Battery Example 1, which was prepared again. Representative discharge curves from this test are shown in FIG. 4 as curve “4”.

Battery Example 5 was identical to Battery Example 1 except that 10% by weight of APC1 was present. Battery Example 5 was tested in the same manner as Battery Example 1 and Battery Example 4 which were prepared again. Representative discharge curves from this test are presented as curve “5” in FIG. 4.

For comparison, Comparative Sample A (control without phosphorus-containing additive) was prepared again and evaluated in the same manner as above. Representative discharge curves from this test are presented as curve “A” in FIG. 4.

As can be seen in FIG. 4, Battery Examples 1, 4 and 5, respectively, had much better performance than Comparative Sample A in the discharge test, despite the presence of phosphorus-containing additives.

Thermal stability of the electrolyte solution of Comparative Sample A and Battery Example 1 was tested using a differential scanning calorimeter (DSC) in the presence of a charged LiCoO ₂ cathode material. The electrolyte of Comparative Sample A exhibited a large exotherm starting at about 220 ° C., indicating that excess thermal decomposition started at this temperature. The electrolyte solution of Battery Example 1 showed no exotherm until reaching a temperature of about 250 ° C., and released much less heat than that emitted by the control. Thus, adding APC1 at a 5% loading not only increases the onset temperature of pyrolysis but also reduces the rate of heat release during pyrolysis.

Example  6 to 9

Battery Example 1 was prepared again and subjected to 100 1C charge / discharge cycles. The specific capacity of this battery was measured at each cycle. At the end of 100 charge / discharge cycles, the specific capacity of Battery Example 1 dropped to about 58% of the starting capacity.

Battery Example 6 was prepared and tested in the same manner as in Battery Example 1, except that the battery electrolyte contained 0.2% by weight of the phosphorus-sulfur compound of Formula XXVI. After 100 1C charge / discharge cycles, the cell maintained about 75% of its starting capacity. Thus, even small additions of such phosphorus-sulfur compounds appear to provide a significant advantage in capacity retention.

Battery Example 7 was prepared and tested in the same manner as in Battery Example 1, except that the battery electrolyte contained 0.2% by weight of the phosphorus-sulfur compound of Formula XXXIV. After 100 1C charge / discharge cycles, the cell maintained about 81% of its starting capacity. Again, these phosphorus-sulfur compounds also appear to offer significant advantages in capacity retention.

Battery Example 8 was prepared and tested in the same manner as in Battery Example 1 above, except that the battery electrolyte contained 2.0% by weight of vinylidene carbonate. After 100 1C charge / discharge cycles, the cell maintained about 78% of its starting capacity.

Battery Example 9 was prepared and tested in the same manner as in Battery Example 1, except that in this case the battery electrolyte contained 2.0% by weight of 1,3-propane sultone. After 100 1C charge / discharge cycles, the cell maintained about 76% of its starting capacity.

With the samples of the battery examples 1 and 6 again prepared, 200 1C charge / discharge cycles were performed. The thermal stability of each electrolyte was evaluated as described above. The electrolyte solution from Battery Example 1 exhibited exotherm at a temperature range of about 235 to 260 ° C., and Battery Example 6 exhibited exotherm at about 280 ° C. These data show that the presence of the phosphorus-sulfur compound in addition to the aromatic phosphate compound increases the thermal stability of the electrolyte after a cycle. These results were obtained without attempting to optimize the overall cell performance by selecting an optimized electrode structure or capacity balance.

Example  10 to 12

The cell (Example 10) was prepared in the same manner as described for Battery Example 1 above except that the electrolyte contained 6% by weight of APC1 and was treated in a formation cycle. The cell was then charged with a constant current to 4.2 V at 1 C rate, and then discharged to a potential of 4.2 V while the current dropped to C / 10. The cell was dismantled in a manner that did not cause a short circuit under an argon atmosphere. The electrode was washed with diethylcarbonate solvent to remove residual salts and electrolyte and dried under vacuum. Under argon, approximately equal weights of electrode and recovered electrolyte were loaded onto the DSC pan and sealed. This sample was treated with DSC. Similar to Example 1, these materials showed no exotherm up to about 250 ° C., with a major exothermic peak at about 290 ° C.

Battery Example 11 was prepared and tested in the same manner as in Example 10, except that the battery electrolyte contained only 3% of APC1 and 3% of the following structural formula.

In the DSC test, this material showed a moderate exotherm at about 240 ° C., and a sharper exotherm near 300 ° C.

Battery Example 12 was prepared and tested in the same manner as in Example 10, except that the battery electrolyte contained only 3% of APC1 and 3% of the following structural formula.

In the DSC test, this material showed a moderate exotherm at about 240 ° C., similar to Example 11 above, a sharper exotherm near 300 ° C.

Examples 10-12 all showed very similar performance in the speed performance test.

Fresh cell electrolytes for electrolytes 10-12 were stored for 9 weeks at room temperature in sealed bottles. The electrolyte of Example 10 became very cloudy during storage, but the electrolytes of Examples 11 and 12 remained transparent. The presence of a mixture of aromatic phosphorus compounds appears to improve the storage stability of the electrolyte.

Claims (22)

A battery electrolyte comprising at least one lithium salt and a non-aqueous solvent in which the lithium salt is dissolved,
A battery electrolyte wherein 0.01 to 80% by weight of the battery electrolyte is at least one aromatic phosphorus compound of formula I:
(I)

Where
A ¹ is a radical containing one or more aromatic rings,
Each R is, independently, an alkylene divalent radical which may contain 1 to 3 carbon atoms and is directly bonded to the carbon atom of the aromatic ring of the A ¹ group,
R ¹ is each independently hydrogen, halogen, OH, a hydrocarbyl group having 12 or less carbon atoms, or an alkoxyl group having 12 or less carbon atoms, or a ring structure in which two R ¹ groups attached to the same phosphorus atom together contain a phosphorus atom Form the
x is an integer of 2 or more. The method of claim 1,
The battery electrolyte solution, in which R ¹ is each an alkoxyl group having 1 to 4 carbon atoms. The method according to claim 1 or 2,
The battery electrolyte wherein R is methylene, ethylene or isopropylene, respectively. The method according to any one of claims 1 to 3,
A battery electrolyte in which the aromatic phosphorus compound has a structure of Formula III:
[Formula III]

Where
R ³ are each independently, hydrogen, C _{1 -3} alkyl, hydroxyl, alkoxyl, halogen, C 1 -C 3 alkenyl, or C _{2 -3} alkylene,
Each R is independently an alkylene divalent radical having 1 to 3 carbon atoms,
Each R ¹ is independently hydrogen, halogen, OH, a hydrocarbyl having 12 or less carbon atoms, or an alkoxyl group having 12 or less carbon atoms, or two R ¹ groups attached to the same phosphorus atom together form a ring structure containing a phosphorus atom Forming,
x is an integer of 2 or more. The method of claim 4, wherein
A battery electrolyte in which the aromatic phosphorus compound has a structure of Formula IV:
[Formula IV]

Where
R ³ are each independently, hydrogen, C _{1 -3} alkyl, hydroxyl, alkoxyl, halogen, C 1 -C 3 alkenyl, or C _{2 -3} alkylene,
R ^{4 's} are each independently alkyl or alkylene having 1 to 8 carbon atoms. The method of claim 5, wherein
Each R ⁴ is independently methyl, ethyl or isopropyl,
Are each independently R ^3, hydrogen or a C _{1 -3} alkyl, battery electrolyte. The method of claim 4, wherein
A battery electrolyte in which the aromatic phosphorus compound has a structure of Formula V:

Where
R ³ is independently, hydrogen, C _{1 -3} alkyl, hydroxyl, alkoxyl, halogen, C 1 -C 3 alkenyl, or C _{2 -3} alkylene,
R ^{4 's} are each independently alkyl having 1 to 8 carbons. The method of claim 7, wherein
Each R ⁴ is independently methyl, ethyl or isopropyl,
Are each independently R ^3, hydrogen or a C _{1 -3} alkyl, battery electrolyte. The method of claim 1,
A battery electrolyte, wherein the aromatic phosphorus compound has a structure of the following formula (VI).
(VI)

The method of claim 1,
A battery electrolyte wherein the aromatic phosphorus compound has a structure of the following general formula (X).
[Formula X]

The method according to any one of claims 1 to 3,
A battery electrolyte containing two or more aromatic phosphorus compounds of formula III:
[Formula III]

Where
R ³ are each independently, hydrogen, C _{1 -3} alkyl, hydroxyl, alkoxyl, halogen, C 1 -C 3 alkenyl, or C _{2 -3} alkylene,
Each R is independently an alkylene divalent radical containing 1 to 3 carbon atoms and directly bonded to the carbon atom of the aromatic ring of said A ¹ group,
Each R ¹ is independently hydrogen, halogen, OH, a hydrocarbyl having 12 or less carbon atoms, or an alkoxyl group having 12 or less carbon atoms, or two R ¹ groups attached to the same phosphorus atom together form a ring structure containing a phosphorus atom Forming,
At least one of the aromatic phosphorus compounds, x is 3 or more,
At least one of the aromatic phosphorus compounds has x 2. The method according to any one of claims 1 to 11,
Wherein said solvent comprises at least one material selected from linear alkyl carbonates, cyclic carbonates, esters, alkyl ethers, nitriles, sulfones, sulfolanes, siloxanes and sultones. The method of claim 12,
A battery electrolyte, wherein the solvent comprises one or more linear alkyl carbonates, one or more cyclic carbonates, or mixtures thereof. The method according to any one of claims 1 to 13,
The lithium electrolyte is at least one of LiPF ₆ , LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ and Li [(CF ₃ SO ₃ ) ₂ N]. The method according to any one of claims 1 to 14,
A battery electrolyte further comprising at least one other additive selected from solid electrolyte interfacial promoters, cathode protectors, lithium salt stabilizers, lithium deposition improvers, ionic solvation improvers, corrosion inhibitors, wetting agents and viscosity reducing agents. The method according to any one of claims 1 to 15,
A battery electrolyte further comprising at least one compound of formula (XII):
[Formula XII]

Where
R ³ are each independently, hydrogen, C _{1 -3} alkyl, hydroxyl, alkoxyl, halogen, C 1 -C 3 alkenyl, or C _{2 -3} alkylene,
R is an alkylene divalent radical containing 1 to 3 carbon atoms and directly bonded to the carbon atom of the aromatic ring of said A ¹ group,
Each R ¹ is independently hydrogen, halogen, OH, a hydrocarbyl having 12 or less carbon atoms, or an alkoxyl group having 12 or less carbon atoms, or two R ¹ groups attached to the same phosphorus atom together form a ring structure containing a phosphorus atom Form. The method according to any one of claims 1 to 16,
A battery electrolyte further comprising at least one phosphorus-sulfur compound of formula XIX:
[Formula XIX]

Where
X is oxygen or sulfur, T is a covalent bond, oxygen or sulfur, provided that at least one of X and T is sulfur,
Each X 'is independently oxygen or sulfur,
each m is independently 0 or 1 when X 'is oxygen, 0, 1 or 2 when X' is sulfur,
n is 1 or more, preferably 2 or more,
Each R ⁵ is, independently, an unsubstituted or inactively substituted hydrocarbyl group, or the R ⁵ groups together form an unsubstituted or inactively substituted divalent organic group,
A is an organic linking group. The method according to any one of claims 1 to 17,
A battery electrolyte further comprising at least one carbonate compound having an aliphatic carbon-carbon unsaturated group. The method according to any one of claims 1 to 17,
A battery electrolyte further comprising at least one sultone compound. A battery comprising an anode, a cathode, a separator disposed between the anode and the cathode, and an electrolyte in contact with the anode and the cathode, wherein the electrolyte is a battery electrolyte according to any one of claims 1 to 19. . The method of claim 20,
A battery, wherein said battery is a secondary battery. 22. The method according to claim 20 or 21,
The battery, wherein the battery is a lithium ion battery, a lithium sulfur battery, a lithium metal battery or a lithium polymer battery.

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